1. Field of the Invention
The present invention relates to an apparatus for driving a turbo supercharger at high efficiency in an internal combustion engine.
2. Description of the Prior Art
A system or an apparatus for rotating an exhaust gas turbine by exhaust gas energy to drive a supercharger and prepressurizing suction gas is known Recently, such systems have been frequently employed in automotive engines.
The conventional turbo supercharger normally employs only one stage of a centrifugal turbine to convert kinetic energy produced by feeding part or all of exhaust gas discharged from the combustion chamber of an engine to an exhaust gas turbine, into rotary motion as the power of the supercharging compressor. The supercharging turbine prepressurizes intake gas and charges vaporized fuel enhanced in its density to a combustion chamber.
In the conventional system, the following problems arise:
1) There is a time lag until a turbo effect is exhibited. PA0 2) Since it is driven only by a positive pressure, its criterion is low and the capacity of the turbine cannot be sufficiently produced. PA0 5) Engine overheating rate is high.
3) Since prepressurized intake gas is superheated by high temperature equipment, its density is low and its charging efficiency is deteriorated.
4) Since it is driven only by high temperature exhaust gas, the equipment becomes heated to an extremely high temperature which is dangerous.
In view of discussions of these factors, the time lag in the above paragraph 1) is considered to result from the fact that, the turbine is rotated at a low speed in the initial operation, and the exhaust gas pressure (back pressure) is insufficient and therefore the starting torque of the exhaust gas turbine is insufficient. The problem in the above paragraph 2) is considered to be that only one direction of the exhaust gas flow acts on the turbine. When the exhaust gas turbine is driven by the exhaust gas energy, the accuracy of the turbine blades is affected, irregular speed distribution and surging occur, and the exhaust gas discharging efficiency after passing the turbine is remarkably reduced by the long duct of an exhaust gas system, catalyst, a silencer, etc. The problem in the above paragraph 3) is considered to be that, particularly in the case of a gasoline engine, decrease in the average effective pressure (Pm) is strongly affected due to the reduction in the air density due to high temperature exhaust gas to cancel the boosting effect. Cooling of suction gas is required to cope with the decrease in the air density. The overheat occurs when the entire engine tends to be constantly overheated, and the influence of the circulated heat of the exhaust gas and the retained heat due to low discharge efficiency are considered.
As results of the above discussions, the present inventor has repeatedly studied the advantages of driving a supercharger with exhaust gas energy. Then, a conclusion has been reached that the driving system is malfunctioned only by the kinetic energy of the exhaust gas flow outputted from a combustion chamber. One of the reasons is that, if the exhaust gas energy at high speed exceeding a sonic speed can be utilized, the problem can be relatively reduced, but since large load resistance is incorporated at the rear in fact, the energy cannot be sufficiently utilized. In other words, if the exhaust gas efficiency is equivalent to that in a system having no other resistances such as catalyst, silencer, etc., this problem can be solved. If the exhaust gas efficiency can be improved. the problem of the heat retention can be alleviated, and the overheating problem can be eliminated.